js socket.emit

io.to(socketid).emit('message', 'whatever');

const socket = io('ws://localhost:3000');
socket.on('connect', () => {  
  // either with send()  
  socket.send('Hello!');
  // or with emit() and custom event names  
  socket.emit('salutations', 'Hello!', { 'mr': 'john' }, Uint8Array.from([1, 2, 3, 4]));});
// handle the event sent with socket.send()
socket.on('message', data => {
  console.log(data);
});
// handle the event sent with socket.emit()
socket.on('greetings', (elem1, elem2, elem3) => {
  console.log(elem1, elem2, elem3);
});

<script src="/socket.io/socket.io.js"></script>
<script>
  const socket = io();
</script>

const socket = new WebSocket('ws://localhost:3000');socket.onopen(() => {  socket.send('Hello!');});socket.onmessage(data => {  console.log(data);});